1. Field of the Invention
The present invention relates to semiconductor wafer polishing, buffing, and cleaning and, more particularly, to techniques for applying liquids over a polishing belt in a Chemical-Mechanical Polishing (CMP) system.
2. Description of the Related Art
In the fabrication of semiconductor devices, there is a need to perform Chemical-Mechanical Polishing operations, including polishing, buffing, cleaning, and planarization of semiconductor wafers. Typically, integrated circuit devices are in the form of multi-level structures. At the substrate level, transistor devices having diffusion regions are formed. In subsequent levels, interconnect metallization lines are patterned and electrically connected to the transistor devices to define the desired functional device. As is well known, patterned conductive layers are insulated from other conductive layers by dielectric materials, such as silicon dioxide. As more metallization levels and associated dielectric layers are formed, the need to planarize the dielectric material increases. Without planarization, fabrication of additional metallization layers becomes substantially more difficult due to the higher variations in the surface topography. In  other applications, metallization line patterns are formed in the dielectric material, and then metal CMP operations are performed to remove excess metallization.
In the prior art, CMP systems typically implement belt, orbital, or brush stations in which belts, pads, or brushes are used to scrub, buff, polish, and planarize one or both sides of a wafer. Slurry is used to facilitate and enhance the CMP operation. Slurry is most usually introduced onto a moving preparation surface, e.g., belt, pad, brush, and the like, and distributed over the preparation surface as well as the surface of the semiconductor wafer being buffed, polished, or otherwise prepared by the CMP process. The distribution is generally accomplished by a combination of the movement of the preparation surface, the movement of the semiconductor wafer and the friction created between the semiconductor wafer and the preparation surface.
FIG. 1A illustrates an exemplary prior art CMP system 100. The CMP system 100 in FIG. 1A is a belt-type system, so designated because the preparation surface is an endless polishing belt 102 mounted on two drums 104 which drive the belt 102 in a rotational motion as indicated by belt rotation directional arrow 106. A wafer 108 is mounted on a carrier head 110. The carrier head 110 is rotated in direction 112. The rotating wafer 108 is then applied against the rotating polishing belt 102 with a force F transmitted through the carrier head shaft 114 to accomplish a CMP process. Some CMP processes require significant force F to be applied. A platen 116 is provided to stabilize the belt 102 and to provide a solid surface onto which to apply the wafer 108. Slurry 118 composed of an aqueous solution, such as NH4OH or DI containing dispersed abrasive particles is introduced to an application region 120 upstream of the wafer 108. FIG. 1A  illustrates the use of a single point slurry 118 distribution apparatus composed of a single tube 122 having an attached dispensing head 124.
FIGS. 1B and 1C illustrate a prior art manifold-type slurry distribution apparatus 150 that has been used as an alternative to the single point slurry distribution apparatus. The lower region of the manifold 150 has a bore 152 through its length with an input 154 at one end and an output 156 at the other end. A number (approx. 9) of threaded holes 158 extend downward from the bore 152 toward the polishing belt 102. Each threaded hole 158 receives a threaded nozzle 160. The bore-end of each nozzle 160 contains a sapphire orifice 162 which is sized to control the slurry 118 flow. A tube 164 is connected between the bore output 156 and the input of a manual metering valve 166. Another tube 168 is connected to the manual metering valve 166 output and travels through one of several ports 170 at the upper region of the manifold 150. The tube 168 may be placed through any one of the ports 170 depending on where extra slurry 118 is required on the belt 102. The manual metering valve 166 is used to control the slurry flow through tube 168. The manual metering valve 166 may be on, off, or regulated. The slurry 118 is provided to the manifold 150 through an input tube 172 in the direction indicated by arrow 174. Due to the small diameter (e.g., 0.029 inch) of the sapphire orifices 162, the slurry 118 will not enter the nozzles 160 unless the bore 152 is pressurized. The pressurization requirement to initiate flow through the sapphire orifices 162 results in an even flow distribution through each nozzle 160. The sapphire orifices 162, nozzle 160 configuration, and bore 152 pressurization causes the slurry 118 to leave nozzles 160 as drops. The slurry application area 176 resulting from the manifold-type slurry distribution apparatus 150 covers more of the polishing belt 102 width than the application area 120 corresponding to the single point slurry distribution apparatus. 
The primary limitation of the single point slurry distribution apparatus (122 and 124) is its limited slurry application area 120. In the prior art, the manifold-type slurry distribution apparatus 150 was developed to provide a wider, more evenly distributed slurry application area 176. However, there are a number of problems associated with the manifold-type slurry distribution apparatus 150.
The manifold-type slurry distribution apparatus 150 was originally developed to place liquid such as water on a cleaning brush. In the present CMP application, the slurry 118 chemistry, higher density, and higher viscosity relative to water, results in a higher potential for clogging of the extremely small (˜0.029 inch diameter) sapphire orifices 162. Thus, one problem with the prior art is the susceptibility to clogging of the small orifice nozzles 160. Making the diameter larger would have the downside of producing an un-even flow out of each of the nozzles 160.
When slurry 118 dries in the nozzles 160 and sapphire orifices 162, it becomes cemented such that it cannot be easily removed. Attempts to remove dried slurry often result in broken components within the bore 152 such as sapphire orifices 162 and nozzles 160. When these components break in the bore, it is not typically possible to repair the manifold. Thus, the entire manifold 150 must be replaced. In the prior art, the nozzles 160 and sapphire orifices 162 must be machined to satisfy surface finish requirements. The manifold-type slurry distribution apparatus 150 is expensive due to its materials and many machined components. Therefore, servicing difficulties requiring replacement of the manifold-type slurry distribution apparatus 150 are very costly. 
In view of the foregoing, there is a need for a slurry distribution apparatus that avoids the problems of the prior art by minimizing clogging potential, improving serviceability, and decreasing replacement frequency and cost. 